Fabrication of electro-mechanical devices utilizing MEMS technology enables to produce devices with typical dimensions of microns to millimeters. Usually these devices include transducers which enable them to move and sense the environment. One of the most useful transduction techniques for MEMS devices is electro-static. Electro-static transduction is performed by an electric capacitor which has a mechanical degree of freedom. Actuation is achieved by applying voltage or charge on the capacitor that causes opposite charges to extract each other and to the transducer to move. Sensing is achieved by changes of capacitance, such as relative displacement between capacitor plates, which cause a change in voltage or charge over the transducer.
Comb drives are of the most useful electro-static transducers. The comb drive has a mechanical degree of freedom that enables capacitor plates to move in parallel to each other. Moving one plate in parallel to the other changes the overlapping area and so the capacitance, and by that a transduction is made. Comb drives are so useful because they enable large displacement and highly sensitive transduction with comparison to other electro-static transducers.
A popular way to fabricate comb drives is by dry etching techniques and in particular Deep Reactive Ion Etch (DRIE). These fabrication techniques are expensive in the sense that they require expensive fabrication facilities and they are time consuming of the fabrication facilities.
Some useful MEMS devices such as raster scanners or rate gyros include mechanical resonators, with resonant frequency defined by the geometrical and material properties. Occasionally we find the critical dimensions of the mechanical resonator with less than order of magnitude larger than the dimensions' tolerances determined by the fabrication processes. In the case of large tolerances in comparison to dimensions there is a very poor accuracy in mechanical properties of the device, such as resonant frequency and spring coefficients. Applications that demand exact resonant frequency, such as raster scanners, must be tuned to the desired frequency.
Many ideas how to tune resonant frequency have been suggested. For example some suggested changing the vibrating mass using a laser beam to melt a metal foil upon the vibrating mass as additive to it. Others suggested changing the vibrating mass using materials that absorbs particles as much as needed. These methods and techniques requires an appropriate apparatus for frequency tuning, which is expensive, it is added to the fabrication apparatus, and often is time consuming. A simple, fabrication process compatible, low cost frequency tuning apparatus is required.